v7.3.0

Added

• Added missing description for the lang argument in TheAudioDB extension.
• Extension schemas now use a gql template tag, which parses them into a GraphQL AST. I didn't use graphql-tag because it currently doesn't support parsing descriptions. Instead I made a very simple tag that just uses graphql.parse(). This tag is exported as graphbrainz/lib/tag for any third-party extensions to use. The benefits of using it are ensuring syntactic correctness, allowing syntax highlighting of the schema literal, and allowing Prettier to format them.